Rotating electric machine having switched or variable reluctance with flux transverse to the axis of rotation

ABSTRACT

An electric machine, such as a switched reluctance motor (SRM), having one or more transverse flux axes is described. The rotor and stator of the electric machine have more than one phase, not necessarily of even number. Flux guidance regions within the stator are angularly and spatially located such that they may be transverse, or not coinciding with, the plane perpendicular to the axis of shaft rotation. The flux guidance regions are composed so as to contain a magnetic field whose flux is guided in either a loop or coupled configuration. In the loop configuration, multiple flux guidance paths that are able to operate simultaneously exist within each chuck arrangement. In the coupled configuration, a single primary flux guidance path exists within the chuck arrangement. Transverse flux guidance allows for the removal and replacement of stator windings without significant disassembly or removal of the motor.

This continuation application claims priority to co-pending U.S. patentapplication Ser. No. 11/128,823 entitled ROTATING ELECTRIC MACHINEHAVING SWITCHED OR VARIABLE RELUCTANCE WITH FLUX TRANSVERSE TO THE AXISOF ROTATION filed May 13, 2005.

FIELD

This invention relates to the field of electric machines, includingelectric motors and generators. More particularly, this inventionrelates to switched and variable reluctance machines, such as a switchedreluctance motor (SRM) or generator, or a variable reluctance motor(VRM) or generator, having one or more transverse flux axes.

BACKGROUND

The conventional switched reluctance motor has been around for well overa century. However, commercial viability and widespread utilization ofthe SRM has been hindered in recent decades for various reasonsincluding poor control techniques, excessive audible noise, and largetorque ripple. Despite these disadvantages, the SRM is of interest dueits relatively simple construction and resulting lower cost whencompared to other traditional electric motors. Because the traditionalreluctance motor only has stator windings, the points of failure canonly be the windings and shaft bearings. This provides for higherreliability. Additionally, with sufficient phase count the traditionalSRM is able to function in the event of a phase failure as there is noflux linkage between phases to produce back-emf on the failed phase.

The traditional SRM topology, such as shown in FIGS. 17A and 17B, haschanged little from its inception. Essentially, the conventional SRMconsists of a stator 100 with salient teeth 102 a-102 b and currentcarrying windings (not shown) that are used to produce flux in a paththat links through rotor teeth 104 a-104 b and a rotor yoke 106. Therotor yoke 106 and stator yoke 100 of the traditional SRM areadditionally used for mechanical integrity and rigidity. The fluxlinkages generated between the stator and rotor of a traditionalswitched reluctance motor are designed to link primarily in plane(s)perpendicular to the axis 108 of shaft rotation and in the plane 110 ofrotor rotation (i.e. radial gap motors). A similar process occurs foraxial gap motors except that the flux linkages generated between thestator and rotor of the traditional SRM link primarily in paths parallelto the axis 108 of shaft rotation and perpendicular to the plane 110 ofrotor rotation.

For example, as shown in FIGS. 17A and 17B, the primary flux path 103 ofthe traditional SRM is through the salient stator teeth 102 a, salientrotor teeth 104 a, the rotor yoke 106, an opposing salient rotor tooth104 b, an opposing salient stator tooth 102 b, the stator yoke 100 andback through the originating stator tooth 102 a. This flux path lieswithin a plane 110 that is perpendicular to the axis of shaft rotation.

A common variation to the reluctance motor design is the stacking ofmultiple reluctance motors, end to end, along a common shaft, at angularoffsets so as to increase the magnitude of the generated torque andreduce torque ripple.

Numerous schemes for increasing the controllability of the traditionalreluctance motor have been implemented. These schemes vary frominnovative control algorithms to novel tooth designs. In one schemedescribed in U.S. Pat. No. 6,700,272, the motor runs at high speeds yetproduces low shaft revolutions per minute (RPM). This allows for reducedtorque ripple and results in a shaft RPM usable by most applications,thereby eliminating the need for a gearbox. This particular method hasbeen accomplished through the introduction of differing flux guidancepaths that result in a planetary gear effect between the rotor andstator. Despite this, the overall motor topology and planar torqueproduction method is not different from that of the traditional SRM.

No known prior SRM design schemes have altered the fundamental design ofthe reluctance motor such that the path of the flux linkage through arotor tooth is variable with position.

SUMMARY

The switched or variable reluctance motor of the present invention has aprimary flux path passing through the center of a stator chuck, througha pole of the stator chuck, through a rotor tooth, through acomplimentary stator chuck, through another rotor tooth, and finallythrough either the originating chuck pole or a different chuck pole.This flux path lies in planes that may be transverse to (not coincidingwith) the plane that is perpendicular to the axis of shaft rotation.While this flux path may include the plane perpendicular to the axis ofshaft rotation, this perpendicular plane is not the sole flux pathplane. With such a flux path, the motor generates or consumes usefultorque with increased use of the volume of the motor, providing forsmaller motors and increased energy density.

The flux generated by the present invention links the angular positionsof the chuck arrangements. Unlike in prior art SRM designs, thepredominate flux flow in the present invention is not through the mainrotor yoke or stator body. Instead, flux is predominately guided withinthe respective rotor teeth and stator chucks. In transferring the fluxpath and the resulting torque to a plane that is transverse to the axisof shaft rotation and independent of the respective yokes, the motorwindings are made accessible for easy removal and replacement duringmotor maintenance.

A preferred embodiment of the invention provides an electric machinecomprising a rotor assembly and one or more stator chuck arrangementsdisposed around and adjacent the rotor assembly. The rotor assemblyincludes a rotor hub and a plurality of rotor teeth. The rotor hub isdisposed in a rotational plane that is substantially perpendicular tothe rotational axis. The rotor teeth are affixed to the rotor hub andare disposed in a substantially circular path about the rotational axis.The rotor teeth include at least a first rotor tooth, a second rotortooth and a third rotor tooth. Each stator chuck arrangement comprisesmultiple stator chuck sets including a first stator chuck set and asecond stator chuck set. Each stator chuck set includes a first statorchuck and an opposing second stator chuck. The first and second statorchucks each have a first chuck pole, a second chuck pole and a chuckwinding, where the first and second chuck poles are disposed adjacentthe rotor teeth as the rotor assembly rotates about the rotational axis.

During operation of this preferred embodiment of the electric machine, aflux path passes from the first chuck pole of the first chuck of thefirst stator chuck set into the first rotor tooth, through the firstrotor tooth and into the first chuck pole of the second stator chuck ofthe first stator chuck set. The flux path further passes from the firstchuck pole of the second stator chuck of the first stator chuck set tothe second chuck pole of the second stator chuck of the first statorchuck set, and from the second chuck pole of the second stator chuck ofthe first stator chuck set into the second rotor tooth.

During operation of one preferred embodiment, the flux path also passesthrough the second rotor tooth and into the second chuck pole of thefirst stator chuck of the first stator chuck set, and from the secondchuck pole of the first stator chuck of the first stator chuck set tothe first chuck pole of the first stator chuck of the first stator chuckset.

During operation of another preferred embodiment, the flux path alsopasses through the second rotor tooth and into the second chuck pole ofa first stator chuck of the second stator chuck set, from the secondchuck pole of the first stator chuck of the second stator chuck set tothe first chuck pole of the first stator chuck of the second statorchuck set, and from the first chuck pole of the first stator chuck ofthe second stator chuck set into the third rotor tooth.

In some preferred embodiments, the stator chuck sets of one or more ofthe stator chuck arrangements are disposed in a substantiallycylindrical relationship about the axis of rotation. In someembodiments, the stator chuck sets of one or more of the stator chuckarrangements are disposed in a substantially conical relationship aboutthe axis of rotation.

In some embodiments, multiple-layer or tiered rotor tooth arrangementsand flux paths are possible. Thus the rotor hub may hold more than oneset and/or layers of rotor teeth, thereby giving rise to increasedstator chuck arrangements and potentially complex flux paths.Additionally, stacking multiple embodiments of the invention end-to-endis possible as is typically done with existing SRM configurations.

In another aspect, the invention provides an electric machine thatincludes a rotor assembly comprising a plurality of rotor teeth disposedat least partially within the rotational plane and substantially in acircular path centered on the rotational axis of the machine. Theelectric machine also includes multiple stator chuck sets that eachinclude a first stator chuck and a second stator chuck. The first statorchuck of each stator chuck set is disposed on an opposite side of therotational plane from the second stator chuck. During operation of theelectric machine, a portion of a flux path passes from the first statorchuck through a rotor tooth to the opposing second stator chuck.

In yet another aspect, the invention provides an electric machinecomprising a rotor assembly, multiple stator chuck sets and a statorhousing. The rotor assembly comprises a plurality of rotor teethdisposed at least partially within the rotational plane of the machineand substantially in a circular path centered on the rotational axis ofthe machine. Each stator chuck set comprises a first stator chuck and asecond stator chuck disposed on opposite sides of the rotational planefrom each other. The stator housing supports the stator chucks in fixedpositions relative to the rotor assembly in such a manner that eachstator chuck may be removed from the stator housing independently ofeach of the other stator chucks.

In general, the basic theory and analysis of the SRM of the presentinvention are similar to that of conventional SRM's. However, therevolved windings and other aspects of the invention provide better useof the three dimensional space thereby providing increased energydensity. With increased energy density, the invention provides a motorthat may be smaller and lighter in weight while still providing powerand torque equivalent to much larger conventional motors.

Another advantage of the present invention is that it allows forenhanced maintainability of the motor. In the preferred embodiment,individual stator chucks/windings may be easily removed and replaced,thereby eliminating the necessity of completely rewinding the wholemotor. Thus, repairs may be done with the motor in its operationalposition, thereby avoiding a long-term interruption in the motoroperation. In fact, with sufficient controls and design considerations,it may be possible to repair the motor while it is operating. Motorperformance may suffer somewhat during such a repair process, but themotor could continue to operate.

In traditional SRM's, acoustic noise can be a significant problem. Onesource of acoustic noise is aerodynamic turbulence introduced by thesalient teeth moving through the air (windage). In the presentinvention, turbulence noise is significantly reduced because theaerodynamic profile of the rotor hub/housing can be made to match theprofile of the tooth structure.

Another source of acoustic noise in traditional SRM's is planar loadingdue to high normal forces acting on the stator housing. In thetraditional SRM design, during flux rise for each phase these normalforces act on opposing stator pole pairs which tends to “squeeze” thestator housing. During flux decline for each phase, the normal forcesacting on the opposing pole pairs are reduced which allows the statorhousing to “relax.” This periodic squeezing and relaxing causes thestator housing to vibrate which adds to the acoustic noise. Unliketraditional SRM's, the loading of the stator housing of the presentinvention is primarily transverse to the plane of rotation so that theinduced stresses do not traverse through the entire housing. Thislocalizes the loading on the stator housing, thereby significantlyreducing acoustic noise.

Another advantage of the present invention is that non-symmetric polepairs are possible, (a pseudo half-arrangement or half-phase ispossible) which could be used to increase the controllability of themotor during transitions between phases.

Also, the novel topology of the present invention could easily beincorporated into a linear SRM or VRM design. While the arrangementsshown in the present invention have been configured such that theyencircle a shaft, the transverse nature of torque production couldeasily be arranged in a linear or three dimensional spline path design.

This novel topology also has relevance to magnetically actuatedvibrating equipment. Typically, vibrating equipment utilizeselectromagnets to attract magnetically conductive material, either ofwhich may be coupled to a load. The spacing between the electromagnetsand magnetically conductive material is typically set prior tooperation, and is done so based upon a known load range. Should the loaddecrease, the electromagnet may produce to much force causing disruptionin the application and/or damage from contact between the electromagnetand magnetically conductive material. As this design surrounds andencloses the magnetically conductive material, longer, smoother strokesare possible and would not have to be spaced based upon existing loads.

Although the description of the invention focuses on preferredembodiments of a switched reluctance motor, it will be appreciated thatvarious aspects of the invention also apply to switched reluctancegenerators as well as variable reluctance motors and generators. Thus,the novel topology of the invention is applicable generally to switchedreluctance machines, variable reluctance machines, including motors andgenerators.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are made apparent by reference tothe detailed description in conjunction with the figures, whereinelements are not to scale so as to more clearly show the details,wherein like reference numbers indicate like elements throughout theseveral views, and wherein:

FIGS. 1A, 1B and 1C depict a rotor assembly according to a preferredembodiment of the invention;

FIGS. 2A and 2B depict a rotor tooth according to a preferred embodimentof the invention;

FIGS. 3A and 3B depict two configurations of a chuck set with phasewindings according to a preferred embodiment of the invention;

FIGS. 4A, 4B, 5A and 5B depict a portion of a stator chuck arrangementsurrounding a rotor assembly according to a preferred embodiment of theinvention;

FIGS. 6A, 6B and 6C depict a stator chuck arrangement surrounding arotor assembly according to a preferred embodiment of the invention;

FIGS. 7A, 7B and 7C depict side views of three separate stator chuckarrangements, each surrounding a rotor assembly according to a preferredembodiment of the invention;

FIGS. 8A, 8B and 8C depict perspective views of three separate statorchuck arrangements, each surrounding a rotor assembly according to apreferred embodiment of the invention;

FIGS. 9A and 9B depict side and perspective views of a motor assemblycomprising three stator chuck arrangements surrounding a single rotorassembly according to a preferred embodiment of the invention;

FIGS. 10A and 10B depict perspective views of a motor assemblycomprising three stator chuck arrangements surrounding a single rotorassembly according to a preferred embodiment of the invention;

FIGS. 11A and 11B depict two views of a chuck arrangement surrounding arotor assembly to provide a loop flux path according to a preferredembodiment of the invention;

FIGS. 12A and 12B depict two views of a chuck arrangement surrounding arotor assembly to provide a coupled flux path according to a preferredembodiment of the invention;

FIGS. 13A-13F depict various views of a stator housing according to apreferred embodiment of the invention;

FIG. 14 depicts three chuck arrangements surrounding a rotor assembly toprovide a loop flux path according to a preferred embodiment of theinvention;

FIG. 15 depicts three chuck arrangements surrounding a rotor assembly toprovide a coupled flux path according to a preferred embodiment of theinvention;

FIG. 16 depicts rotation of flux direction in a rotor tooth duringoperation of a switched reluctance machine having three chuckarrangements according to a preferred embodiment of the invention; and

FIGS. 17A and 17B depict an example of a conventional switchedreluctance motor.

DETAILED DESCRIPTION

As shown in FIGS. 1A-1C, a preferred embodiment of the inventionincludes a rotor assembly 2 comprising a rotor hub 4 and multiple rotorteeth 6. The primary purpose of the rotor hub 4 is to hold the rotorteeth 6 and mechanically couple the rotor teeth 6 to a shaft. Becausethe path of the flux linkage of the preferred embodiment does notcoincide with the plane of the rotor hub 4, the rotor hub 4 need not beelectrically or magnetically conductive. Thus, the hub 4 may be formedfrom practically any material that provides the desired structuralrigidity, such as, plastic, metal or composite materials. There may bemultiple sets of rotor teeth 6 located at various spatial and angularoffsets that are held fixed by the one or more rotor hubs 4. Therefore,the invention is not limited to any particular rotor tooth arrangement.

In the present invention, the flux linkages that produce the usefultorque are made between a stator and the rotor teeth 6—not through arotor yoke as is done in conventional SRM's. As shown in FIGS. 1A-1C,the rotor teeth 6 of the present invention are designed such that theirspatial and angular offsets are symmetrical. As shown in FIGS. 2A and2B, each tooth 6 may be described as a segment of a toroid. The outsidesurface of each rotor tooth 6 has a finite number of faces 8. In analternative embodiment, the outer surfaces of the rotor teeth 6 aresmooth, as with a typical toroidal shape.

FIGS. 3A-3B depict two configurations of stator chuck sets 12 a and 12 bwhich surround the rotor teeth 6. Each stator chuck set 12 a, 12 bcomprises two opposing stator chucks 10. As shown in FIGS. 4A-4B, 5A-5B,6A-6C, 7A-7C, 8A-8C, 9A-9B and 10A-10B, each of the stator chucks 10 isangularly and spatially offset from the rotor teeth 6 and from each ofthe other stator chucks 10. As shown in FIGS. 3A and 3B, each chuck 10preferably includes a chuck center 10 a and two chuck poles 10 b. Aboutthe center 10 a of each stator chuck 10 is secured a winding 11 or otherflux production means. It will be appreciated that FIGS. 4A-4B and 5A-5Bshow only the outer (larger) of the chucks 10 of each chuck set 12 a.

During operation of the motor, flux linkages develop between one or morechucks 10, through one or more rotor teeth 6, and into one or moreopposing chucks 10. Thus, the stator chucks 10 are the primary conduitfor the stator flux. The chuck poles 10 b are profiled such that eachpole has a face 10 c-10 d that is parallel to a corresponding rotortooth face 8.

As shown in FIGS. 6A-6C, 7A-7C and 8A-8C, each stator chuck arrangement14 a, 14 b, 14 c consists of one or more complimentary chuck sets 12a-12 b that enclose and surround the rotor teeth 6. Complimentary chucksets 12 a-12 b in a chuck arrangement 14 a, 14 b, 14 c need not be inparallel, nor do they need to be symmetrically located about the rotorteeth 6 or to other chucks sets 12 a-12 b. Additionally, complimentarychuck sets 12 may have an odd or even number of chucks 10.

In a preferred embodiment of the invention depicted in FIGS. 7A-7C and8A-8C, the motor comprises three stator chuck arrangements 14 a, 14 b,14 c that are angularly offset and spatially offset from each other. Thestator chuck arrangements 14 a, 14 b, 14 c may or may not overlap otherstator chuck arrangements 14 a, 14 b, 14 c. Should they overlap, thenduring operation, direct flux linkage paths exist between the rotorteeth 6 and one or more of the stator chuck arrangements 14 a, 14 b, 14c. In addition, stator chuck arrangements 14 are angularly and spatiallypositioned such that flux through any stator chuck 10 may link throughone or more rotor teeth 6. Although the preferred embodiment of theinvention includes three stator chuck arrangements 14 a, 14 b, 14 c, itshould be appreciated that there may be more or fewer than three thatmay or may not overlap. Therefore, the invention is not limited to anyparticular number of stator chuck arrangements, or angular or spatialoffsets.

FIGS. 9A-9B and 10A-10B depict all three stator chuck arrangements 14 a,14 b, 14 c enclosing and surrounding a single rotor assembly 2 withpartial overlapping of the arrangements. In a preferred embodiment, thestator chuck arrangements 14 a, 14 b, 14 c are held in place by meansintegrated into a stator housing 16, a preferred embodiment of which isdepicted in FIGS. 13A-13F. The stator housing 16 is not depicted inFIGS. 9A and 9B and 10A-10B so that the chuck arrangements 14 a, 14 b,14 c may be clearly shown.

Unlike a traditional SRM design, the preferred embodiment of the statorhousing 16 is not part of the primary flux path or part of anyelectrical conduction path. Thus, the stator housing 16 need onlyprovide mechanical integrity in supporting the stator chuck arrangementsand maintaining their locations with respect to the rotor assembly 2.Preferably, wires or traces for connection of stator chuck windings aswell as desired control elements are integrated into the stator housing16. The housing 16 may be formed from practically any material thatprovides the desired structural rigidity, such as plastic, metal orcomposite materials.

As flux linkage of sufficient magnitude is established between any oneof the stator chuck arrangements (such as 14 a) and the rotor teeth 6,the rotor teeth 6 will tend to align with the flux established betweenthe opposing chuck poles 10 b in the stator chuck arrangement 14 a.Since the rotor teeth 6 are secured to the rotor hub 4, the alignment ofthe teeth 6 to the chuck poles 10 b causes the rotor hub 4 to rotate. Asthe hub 4 rotates, the teeth 6 begin to align with the poles 10 b of anadjacent stator chuck arrangement 14 b which is angularly and spatiallyoffset from the chuck arrangement 14 a. (See FIGS. 10A-10B.) Theadjacent stator chuck arrangement 14 b then begins to establish new fluxlinkages as the flux linkages for the previous chuck arrangement 14 apeak and begin to decay. This process of flux establishment, alignmentof rotor teeth 6 and chuck poles 10 b, flux decay and new fluxestablishment is repeated for continuous rotation and operation. Statorchuck sets 12 a-12 b work cooperatively within the stator chuckarrangements 14 a, 14 b, 14 c. In this way, flux linkage is madesuccessively from one stator chuck arrangement to another. Since thestator chuck arrangements 14 a, 14 b, 14 c are positioned angularly andspatially around the rotor teeth 6, flux linkage, and thus torquegeneration, is made along a three-dimensional path surrounding the rotorteeth 6.

In an alternative embodiment of the invention, chuck arrangements 14 a,14 b, 14 c may have several different configurations. For example, FIGS.11A and 11B show a “loop” configuration. In this configuration fourseparate flux paths 18 exist within each chuck arrangement 14 and theflux paths 18 are localized about four separate center points. In theconfiguration shown in FIGS. 11A and 11B, each flux path 18 involves twostator chucks 10 and two rotor teeth 6 per path. It will be appreciatedthat more or fewer than four flux paths per arrangement may exist in aloop configuration. Thus, the invention is not limited to any particularnumber of flux paths in a loop configuration.

FIG. 14 depicts a plane view representation of the loop configurationshowing the alignment pattern with partial overlapping and the multiplelocalized flux paths 18. Utilization of the loop configuration hasadvantages in applications requiring large load variations. Withsufficient control capabilities, individual chuck set windings within anarrangement could be disengaged so that they no longer produce flux andthus torque. This allows other still operational chuck sets to continueoperating at their peak efficiencies. With sufficient mechanical andcontrol integration, the loop configuration also allows for the removaland replacement of a chuck set, possibly while the motor is still inoperation. This ability to repair the motor without removal or totaldisassembly has significant advantages and benefits, such as maximizedin-service time.

FIGS. 12A-12B show a coupled configuration in which the flux flowsthrough a single primary flux path 18 passing through all the chucks 10and all the rotor teeth 6. FIG. 15 depicts a plane view representationof the coupled configuration showing the alignment pattern with partialoverlapping and the single flux path 18 per chuck arrangement. Thecoupled configuration is beneficial in applications with relativelyconstant loading. Because the flux within a coupled arrangement is inseries, a failure of one winding would result in marginal loss to theoverall arrangement. Thus, with sufficient controls the remainingwindings would need only increase their current level a nominal amountto return to the desired flux linkage magnitude. This would delay theneed for immediate repair thereby allowing the motor to say in servicelonger.

It will be appreciated that some embodiments of the invention maycomprise a combination of the loop and coupled configurations.

Many prior art schemes have a specific flux path passing within rotorteeth. However, the transverse nature of the flux paths of the presentinvention is such that the flux path through the rotor tooth isvariable. Thus, the flux path may be in opposite directions for twodifferent rotor positions or it may be angularly offset. For example,FIG. 16 depicts the sequential process of flux linkage initiation fromone stator chuck arrangement to another during eight stages of operationof an SRM having three chuck arrangements. The arrows indicate theprimary direction of the flux path within a stator tooth from one toothface (such as 8 a) to the opposing tooth face (such as 8 a′). In thecase of overlap of stator chuck arrangements, the previous chuck willhave established flux linkage, such that any new flux linkage may resultin significant mutual inductance. If there is little to no overlap, theprevious primary arrangement may have little effect upon the developinglinkages.

The foregoing description of preferred embodiments for this inventionhave been presented for purposes of illustration and description. Theyare not intended to be exhaustive or to limit the invention to theprecise form disclosed. Obvious modifications or variations are possiblein light of the above teachings. The embodiments are chosen anddescribed in an effort to provide the best illustrations of theprinciples of the invention and its practical application, and tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention as determined by the appendedclaims when interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

1. An electric machine having a rotational axis, the machine comprising:a rotor assembly comprising: a rotor hub disposed in a rotational planethat is substantially perpendicular to the rotational axis; and aplurality of rotor teeth affixed to the rotor hub, the rotor teethdisposed in a substantially circular path about the rotational axis, therotor teeth including at least a first rotor tooth, a second rotor toothand a third rotor tooth; and one or more stator chuck arrangementsdisposed around and adjacent the rotor assembly, each stator chuckarrangement comprising a plurality of stator chuck sets including atleast a first stator chuck set and a second stator chuck set, eachstator chuck set comprising at least a first stator chuck and a secondstator chuck, the first and second stator chucks each having a firstchuck pole, a second chuck pole and a chuck winding, the first andsecond chuck poles being disposed adjacent the rotor teeth as the rotorassembly rotates about the rotational axis, where during operation ofthe electric machine, a flux path passes from the first chuck pole ofthe first chuck of the first stator chuck set into the first rotortooth, through the first rotor tooth and into the first chuck pole ofthe second stator chuck of the first stator chuck set, from the firstchuck pole of the second stator chuck of the first stator chuck set tothe second chuck pole of the second stator chuck of the first statorchuck set, and from the second chuck pole of the second stator chuck ofthe first stator chuck set into the second rotor tooth.